Pectin hydrolysis by certain salt-tolerant yeasts.

During the brine fermentation of cucumbers for pickles, Bell et al. (1950) have reported finding a fungal-type polygalacturonase-like enzyme which splits the polymer linkage of pectic substances. They definitely established this enzyme with the softening type of spoilage of salt-stock pickles brined under commercial conditions. With the identity of the softening agent known, an inquiry into its origin is of interest. The principal possibilities as to source are: the microbiological activity occurring during the curing and subsequent storage in brine, and the nature of the green cucumber fruit that is brined. The present work considers one phase of the first category, namely, the possible relationship of brine yeasts to softening as indicated by their ability to hydrolyze citrus pectin in cultural media. The method used in this study was devised as a rapid screening technique for such biochemical changes of pectin as indicated by a calcium pectate gel or the loss of such gel properties. The changes in pectin are not taken to be specific enzyme measurements for polygalacturonase and pectinesterase; nevertheless, such a screening technique is most valuable for qualitatively identifying yeasts as potential sources of pectic enzymes. Pittman and Cruess (1929) reported on the hydrolysis of a 1 per cent apple pectin by various microorganisms as indicated by change in viscosity, decrease in pectin content, and loss of gelling power of the pectin. The yeast cultures tested-Saccharomyces cerevisiae, Saccharomyces ellipsoideus, and Mycoderma specieswere reported to have no noticeable effect on the pectin. Luh and Phaff (1951) found 6 cultures of yeasts (Saccharomyces fragilis, S. fragilis var. no. 351, Saccharomyces thermantitonum, Torulopsis kefyr, Candida pseudotropicalis var. lactosa, and Candida pseudotropicalis) that were capable of causing a noticeable change in pectin broth containing minerals and glucose. Clarification of the opaque pectin solution to a water-clear liquid with the formation of a sediment was the criterion used to determine hydrolytic action. According to Luh and Phaff, these 6 cultures can all be identified with S. fragilis and a variety of this species, along with its